Plasma processing such as plasma-based ashing, dry etching, thin film deposition, or surface modification is applied to semiconductor manufacturing devices and liquid crystal display manufacturing devices, and widely used in various industrial fields including the electronics industry.
In particular, the “ashing process” for ashing resist using a plasma is often used as a dry process for removing and decomposing the resist used as a mask material in etching or ion implantation for fine patterning.
As a plasma processing device that can be used in such an ashing process, the so-called “down flow type” and “remote plasma type” devices are known.
In the “down flow type” plasma processing device, a generation chamber for generating a plasma and a reaction chamber in which a workpiece is mounted are provided in the same vacuum chamber (see, e.g., JP 5-315292A (1993)). On the other hand, in the “remote plasma type” plasma processing device, a generation chamber for generating a plasma is connected via a transfer pipe to a reaction chamber in which a workpiece is mounted, and thus the device is configured so that the plasma is isolated from the workpiece (see, e.g., JP 2001-189305A and JP 2002-541672T).
FIG. 20 is a schematic view showing an example “down flow type” ashing device. This device has a chamber 110, a transmission window 118 made of a planar dielectric plate provided on the upper face of the chamber 110, a microwave waveguide 120 provided outside the transmission window 118, and a stage 116 for mounting and holding a workpiece W such as a semiconductor wafer in the processing space below the transmission window 118.
This ashing device is used to ash the surface of the workpiece W as follows. The processing space is first depressurized by an evacuation system E. An atmosphere of a processing gas is then formed, where a microwave M is fed from the microwave waveguide 120. The microwave M provides energy to the gas in the chamber 110 via the transmission window 118 and forms a plasma P of the processing gas. In the plasma P, ions and electrons collide with molecules of the processing gas to generate excited active species (plasma products) such as excited atoms, molecules, and free atoms (radicals). These plasma products diffuse in the processing space as represented by arrow A and fly to the surface of the workpiece W, where plasma processing such as etching occurs.
The publication JP 5-315292A discloses a down flow type ashing device of the type described above, where a shower head 400 with a plurality of holes formed therein is provided between the generation chamber for generating a plasma and the reaction chamber in which the workpiece W is mounted. The purpose of this shower head 400 is to allow passage of active particle species of the plasma and to prevent passage of ions.
FIG. 21 is a schematic view showing the relevant part of a “remote plasma type” plasma processing device disclosed in JP 2001-189305A. More specifically, a plasma transfer pipe 130 is connected above a chamber 110. A processing gas G is supplied through the tip of the plasma transfer pipe 130, to which a microwave waveguide 120 is connected and a microwave M is supplied. The microwave M provides energy to the processing gas G to form a plasma P. Active species A such as radicals contained in the plasma P are supplied via the transfer pipe 130 to a workpiece W in the chamber 110, where plasma processing such as ashing thereby occurs.
The publication JP 2002-541672T discloses a plasma generating device in which a transfer pipe 130 includes a right-angle “bend” to avoid direct line of sight extending from glow discharge of plasma P to a downstream chamber 110.
In recent years, an insulation film made of a “low-k material” (a material having a low dielectric constant) has received attention as a constituent technology for achieving higher integration of semiconductor devices. This is a material for use in interlayer insulating films provided between a plurality of interconnect layers or in gate insulating films for insulated gate devices, and has an advantage in its capability of reducing parasite capacitance because of its low dielectric constant. These low-k materials may include, for example, organic materials such as polyimides, and porous silicon oxides.
However, the inventors have recognized as a result of their independent experiments that the workpiece subjected to plasma processing by these conventional devices may be damaged, or otherwise there is room for improvement in the efficiency of plasma processing. More specifically, it is recognized that, when such a low-k material is patterned with a resist mask formed thereon and the resist mask is subsequently ashed, the low-k material is also etched, which has a problem of increasing the dielectric constant and/or parasite capacitance.
The invention is based on the recognition of these problems. An object of the invention is to provide a plasma processing device and an ashing method capable of ashing or other plasma processing for low-k materials and the like without unnecessary damage thereto on the basis of ideas different from conventional technologies.